Na0.33V2O5·1.5H2O nanorings/nanorods and Na0.33V2O5·1.5H2O/RGO composite fabricated by a facile one pot synthesis and its lithium storage behavior

In this work, Na0.33V2O5·1.5H2O nanorings/nanorods and Na0.33V2O5·1.5H2O/reduced graphene oxide (RGO) composites have been prepared through a facile hydrothermal route in acidic medium at 200 °C for 2 days. The hydrothermally derived products have been characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, UV–Visible spectroscopy, Thermogravimetric analysis (TGA), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and electrochemical discharge–charge cycling in lithium ion battery. XRD pattern exhibits the layered structure of Na0.33V2O5·1.5H2O and the composite shows the presence of RGO at 2θ = 25.8°. FTIR spectrum shows that the band at 760 cm− 1 could be assigned to a V-OH2 stretching mode due to coordinated water. Raman spectrum shows that the band at 264 cm− 1 is due to the presence of water molecules between the layers. FESEM/TEM micrographs reveal that the products consist of nanorings of inner diameter 5 μm and thickness of the ring is found to be 200–300 nm. Addition of exfoliated graphene oxide (EGO) destroys the formation of rings. The reduction of EGO sheets into RGO is also evidenced by the red shift of the absorbance peak from 228 nm to 264 nm. In this composite Na0.33V2O5·1.5H2O nanorods may adhere to the surface of RGO and/or embedded in the RGO nanosheets. As a result, an effective three-dimensional conducting network was formed by bridging RGO nanosheets, which can facilitate electron transport effectively and thus improve the kinetics and rate performance of Na0.33V2O5·1.5H2O nanorings/nanorods. The Na0.33V2O5·1.5H2O/RGO composites exhibited a discharge capacity of 340 mAh g− 1 at a current density of 0.1 mA g− 1 and also an improved cyclic stability. RGO plays a ‘flexible confinement’ function to enwrap Na0.33V2O5·1.5H2O nanorods, which can compensate for the volume change and prevent the detachment and agglomeration of pulverized Na0.33V2O5·1.5H2O, thus extending the cycling life of the electrode. A probable reaction mechanism for the formation of Na0.33V2O5·1.5H2O nanorings is also discussed.